1. Field of the Invention
This invention relates to a composition of an organic solid electrolyte and a coloring-discoloring device or color developing changing device resorting to electrochromism as the principle of operation thereof, which incorporates therein the organic solid electrolyte. The term "electrochromism" refers to the phenomenon of a reversible change in color or the transmittance of light caused by the oxidation-reduction reaction occurring on the surface or in the neighborhood of an electrode in response to the application of voltage thereto, for example.
2. Description of the Prior Art
Organic solid electrolytes are fulfilling an important role as an electrolyte for batteries and as an electrolyte for electrochromic devices. The conventional organic solid electrolytes, however, are not fully satisfactory in terms of performance quality, productivity, and price and, therefore, are usable only in limited applications as compared with liquid electrolytes. The color developing-changing devices which use electrochromism are in need of electrolytes excelling in ionic conductivity because their speed of coloration and decoloration is varied by the performance quality of electrolyte used.
The organic solid electrolytes which have been reported to the art to date include those using a polyether as a substrate (published Japanese Patent Application, KOKAI (Early Publication) No. SHO 63-76,273), those using a TCNQ salt (7,7,8,8-tetracyano-p-quinodimethane) (published Japanese Patent Application, KOKAI No. SHO 63-173,314), those using an organopolysiloxane (published Japanese Patent Application, KOKAI No. HEI 2-80,462), and those using a polyethylene glycol (published Japanese Patent Application, KOKAI No. HEI 2-138,364), for example. As clearly indicated in "Handbook of New Macromolecular Compound Materials" (compiled by Polymer Academic Society (Japan) and published by Maruzen Book Co., Ltd. in 1989), however, the development of organic solid electrolytes has been carried out prevalently on composites between polyethylene oxide (PEO) and alkali metal salts and very rarely on other substances.
Heretofore, the color developing-changing devices which operate on the principle of electrochromism have mainly used liquid propylene carbonate as an electrolyte. Propylene carbonate is an excellent electrolyte which has high voltage for inducing electrolysis and possesses ability to dissolve a large amount of salt. When the device uses such a liquid electrolyte as propylene carbonate, however, it requires to be sealed most tightly because the liquid electrolyte is liable to leak. When a solid electrolyte is used, the ionic conductivity thereof is low and the operation of coloration and decoloration consumes a long time, though the possibility of leakage is nil. Since the solid electrolyte, therefore, must be shaped in the form of a thin film, the desirability of this organic solid electrolyte possessing excellent processability has been finding growing recognition.
The conventional organic solid electrolytes mentioned above allow no easy selection of a suitable solvent and suffer from inferior processability on account of high melting points. Particularly, the electrochromic devices using organochromophoric materials are not easily worked at high temperatures. The fabrication of these devices at elevated temperatures proves undesirable because the chromophoric materials yield to decomposition and degradation. Further, the use of polyethylene glycol which has prevailed to date as a substrate for electrolyte is at a disadvantage in lacking strength and necessitating a support for the retention of shape. The use of polyethylene oxide, for example, entails the disadvantage that the ionic conductivity is degraded and the operation of coloration and decoloration is hindered in consequence of the advance of crystallization.